Medical devices for modulating nerves

ABSTRACT

Medical devices and methods for making and using medical devices are disclosed. An example medical device may include a medical device for modulating nerves. The medical device may include an elongate shaft having a distal region. A balloon may be coupled to the distal region. An electrode may be disposed within the balloon. A virtual electrode may be defined on the balloon. The virtual electrode may include a region having a first conductive layer and a second conductive layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 61/776,653, filed Mar. 11, 2013, the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure pertains to medical devices, and methods for manufacturing medical devices. More particularly, the present disclosure pertains to elongated medical devices for modulating nervous system activity.

BACKGROUND

A wide variety of intracorporeal medical devices have been developed for medical use, for example, intravascular use. Some of these devices include guidewires, catheters, and the like. These devices are manufactured by any one of a variety of different manufacturing methods and may be used according to any one of a variety of methods. Of the known medical devices and methods, each has certain advantages and disadvantages. There is an ongoing need to provide alternative medical devices as well as alternative methods for manufacturing and using medical devices.

BRIEF SUMMARY

This disclosure provides design, material, manufacturing method, and use alternatives for medical devices. An example medical device may include a medical device for modulating nervous system activity. The medical device may include an elongated shaft having a distal region. A balloon may be coupled to the distal region. The balloon may have an inner conductive layer, an outer conductive layer, and an intermediate non-conductive layer disposed between the inner layer and the outer layer. An electrode may be disposed within the balloon. A virtual electrode may be defined on the balloon. The virtual electrode may include a conductive region defined along a first portion of the balloon that is free of the intermediate non-conductive layer.

An example method for manufacturing a medical device may include providing an expandable balloon, disposing a mask member on the balloon, coating the balloon with a non-conductive material, removing the mask member, and coating the balloon with a conductive material. A virtual electrode may be defined at a region adjacent to the mask.

The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The Figures, and Detailed Description, which follow, more particularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of the following detailed description in connection with the accompanying drawings, in which:

FIG. 1 is a schematic view illustrating a renal nerve modulation system in situ;

FIG. 2 is a side view of a portion of an example medical device;

FIG. 3 is a cross-sectional view taken through line 3-3 in FIG. 2;

FIG. 4 is a cross-sectional view taken through line 4-4 in FIG. 2;

FIGS. 5-8 illustrate some portions of an example method for manufacturing a medical device;

FIG. 9 is a partial cross-sectional view of an example medical device; and

FIG. 10 is a side view of a portion of an example medical device.

While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

DETAILED DESCRIPTION

For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in this specification.

All numeric values are herein assumed to be modified by the term “about,” whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the terms “about” may include numbers that are rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).

As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

It is noted that references in the specification to “an embodiment”, “some embodiments”, “other embodiments”, etc., indicate that the embodiment described may include one or more particular features, structures, and/or characteristics. However, such recitations do not necessarily mean that all embodiments include the particular features, structures, and/or characteristics. Additionally, when particular features, structures, and/or characteristics are described in connection with one embodiment, it should be understood that such features, structures, and/or characteristics may also be used in connection with other embodiments whether or not explicitly described unless clearly stated to the contrary.

The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention.

Certain treatments require the temporary or permanent interruption or modification of select nerve function. One example treatment is renal nerve ablation, which is sometimes used to treat conditions related to hypertension, congestive heart failure, diabetes, or other conditions impacted by high blood pressure or salt retention. The kidneys produce a sympathetic response to congestive heart failure, which, among other effects, increases the undesired retention of water and/or sodium. Ablating some of the nerves running to the kidneys may reduce or eliminate this sympathetic function, which may provide a corresponding reduction in the associated undesired symptoms.

While the devices and methods described herein are discussed relative to renal nerve modulation, it is contemplated that the devices and methods may be used in other treatment locations and/or applications where nerve modulation and/or other tissue modulation including heating, activation, blocking, disrupting, or ablation are desired, such as, but not limited to: blood vessels, urinary vessels, or in other tissues via trocar and cannula access. For example, the devices and methods described herein can be applied to hyperplastic tissue ablation, cardiac ablation, pulmonary vein isolation, tumor ablation, benign prostatic hyperplasia therapy, nerve excitation or blocking or ablation, modulation of muscle activity, hyperthermia or other warming of tissues, etc. In some instances, it may be desirable to ablate perivascular renal nerves with ultrasound ablation.

FIG. 1 is a schematic view of an illustrative renal nerve modulation system in situ. System 10 may include one or more conductive element(s) 16 for providing power to a renal ablation system including a renal nerve modulation device 12 and, optionally, within a delivery sheath or guide catheter 14. A proximal end of conductive element(s) 16 may be connected to a control and power unit 18, which may supply the appropriate electrical energy to activate one or more electrodes disposed at or near a distal end of the renal nerve modulation device 12. In addition, control and power unit 18 may also be utilized to supply/receive the appropriate electrical energy and/or signal to activate one or more sensors disposed at or near a distal end of the renal nerve modulation device 12. When suitably activated, the electrodes are capable of ablating tissue as described below and the sensors may be used to sense desired physical and/or biological parameters. The terms electrode and electrodes may be considered to be equivalent to elements capable of ablating adjacent tissue in the disclosure which follows. In some instances, return electrode patches 20 may be supplied on the legs or at another conventional location on the patient's body to complete the electrical circuit. A proximal hub (not illustrated) having ports for a guidewire, an inflation lumen and a return lumen may also be included.

The control and power unit 18 may include monitoring elements to monitor parameters such as power, voltage, pulse size, temperature, force, contact, pressure, impedance and/or shape and other suitable parameters, with sensors mounted along renal nerve modulation device 12, as well as suitable controls for performing the desired procedure. In some embodiments, the power unit 18 may control a radiofrequency (RF) electrode and, in turn, may “power” other electrodes including so-called “virtual electrodes” described herein. The electrode may be configured to operate at a suitable frequency and generate a suitable signal. It is further contemplated that other ablation devices may be used as desired, for example, but not limited to resistance heating, ultrasound, microwave, and laser devices and these devices may require that power be supplied by the power unit 18 in a different form.

FIG. 2 illustrates a distal portion of a renal nerve modulation device 12. Here it can be seen that renal nerve modulation device 12 may include an elongate member or catheter shaft 34, an expandable member or balloon 22 coupled to shaft 34, and an electrode 24 disposed within balloon 22. Additional electrodes 24 may also be utilized. When in use, balloon 22 may be filled with a conductive fluid such as saline to allow the ablation energy (e.g., radiofrequency energy) to be transmitted from electrode 24, through the conductive fluid, to one or more virtual electrodes 28 disposed along balloon 22. While saline is one example conductive fluid, other conductive fluids may also be utilized including hypertonic solutions, contrast solution, mixtures of saline or hypertonic saline solutions with contrast solutions, and the like. The conductive fluid may be introduced through a fluid inlet 31 and evacuated through a fluid outlet 32. This may allow the fluid to be circulated within balloon 22. As described in more detail herein, virtual electrodes 28 may be generally hydrophilic portions of balloon 22. Accordingly, virtual electrodes 28 may absorb fluid (e.g., the conductive fluid) so that energy exposed to the conductive fluid can be conducted to virtual electrodes 28 such that virtual electrodes 28 are capable of ablating tissue.

A cross-sectional view of shaft 34 of the renal nerve modulation device 12 proximal to balloon 22 is illustrated in FIG. 3. Here it can be seen that shaft 34 may include a guidewire lumen 36, a lumen 38 connected to the fluid inlet 31, and a lumen 40 connected to the fluid outlet 32. Other configurations are contemplated. In some embodiments, guidewire lumen 36 and/or one of the fluid lumens 38/40 may be omitted. In some embodiments, guidewire lumen 36 may extend from the distal end of device 12 to a proximal hub. In other embodiments, the guidewire lumen can have a proximal opening that is distal the proximal portion of the system. In some embodiments, the fluid lumens 38/40 can be connected to a system to circulate the fluid through the balloon 22 or to a system that supplies new fluid and collects the evacuated fluid. It can be appreciated that embodiments may function with merely a single fluid lumen and a single fluid outlet into the balloon.

Electrode 24 (or a conductive element to supply power to electrode 24) may extend along the outer surface of shaft 34 or may be embedded within the shaft. Electrode 24 proximal to the balloon may be electrically insulated and may be used to transmit power to the portion of the electrode 24 disposed within balloon 22. Electrode 24 may be a wire filament electrode made from platinum, gold, stainless steel, cobalt alloys, or other non-oxidizing materials. These elements may also be clad with copper in another embodiment. In some instances, titanium, tantalum, or tungsten may be used. Electrode 24 may extend along substantially the whole length of the balloon 22 or may extend only as far as the distal edge of the most distal virtual electrode 28. The electrode 24 may have a generally helical shape and may be wrapped around shaft 34. While the electrode 24 is illustrated as having adjacent windings contacting one another, in some instances the windings may be spaced a distance from one another. Alternatively, electrode 24 may have a linear or other suitable configuration. In some cases, electrode 24 may be bonded to shaft 34. The electrode 24 and virtual electrodes 28 may be arranged so that the electrode extends directly under the virtual electrodes 28. In some embodiments, electrode 24 may be a ribbon or may be a tubular member disposed around shaft 34. In some embodiments, a plurality of electrodes 24 may be used and each of the plurality may be fixed to the shaft 34 under virtual electrodes 28 and may share a common connection to conductive element 16. In other embodiments that include more than one electrode, each electrode may be separately controllable. In such embodiments, balloon 22 may be partitioned into more than one chamber and each chamber may include one or more electrodes. The electrode 24 may be selected to provide a particular level of flexibility to the balloon to enhance the maneuverability of the system. It can be appreciated that there are many variations contemplated for electrode 24.

A cross-sectional view of the shaft 34 distal to fluid outlet 32 is illustrated in FIG. 4. The guidewire lumen 36 and the fluid inlet lumen 40 are present, as well as electrode 24. In addition, balloon 22 is shown in cross-section as having a first layer 44, a second layer 46, and a third layer 48. Virtual electrode 28 is formed in balloon 22 by the absence of second layer 46. First and third layers 44/48 may include a hydrophilic, hydratable, RF permeable, and/or conductive material. One example material is hydrophilic polyurethane (e.g., TECOPHILIC® TPUs such as TECOPHILIC® HP-60D-60 and mixtures thereof, commercially available from the Lubrizol Corporation in Wickliffe, Ohio). Other suitable materials include other hydrophilic polymers such as hydrophilic polyether block amide (e.g., PEBAX® MV1074 and MH1657, commercially available from Arkema headquartered in King of Prussia, Pa.), hydrophilic nylons, hydrophilic polyesters, block co-polymers with built-in hydrophilic blocks, polymers including ionic conductors, polymers including electrical conductors, metallic or nanoparticle filled polymers, and the like. Suitable hydrophilic polymers may exhibit between 20% to 120% water uptake (or % water absorption) due to their hydrophilic nature or compounding. In at least some embodiments, first and third layers 44/48 may include a hydratable polymer that is blended with a non-hydratable polymer such as a non-hydratable polyether block amide (e.g., PEBAX® 7033 and 7233, commercially available from Arkema) and/or styrenic block copolymers such as styrene-isoprene-styrene. These are just examples.

The second layer 46 may include an electrically non-conductive polymer such as a non-hydrophilic polyurethane, homopolymeric and copolymeric polyurethanes (e.g., NeoRez R-967, commercially available from NeoResins, Inc. in Wilmington, Mass.; and/or TECOFLEX® SG-85A and/or TECOFLEX SG-60D, commercially available from Lubrizol Corp. in Wickliffe, Ohio), polyether block amide, nylon, polyester or block-copolymer. Other suitable materials include any of a range of electrically non-conductive polymers. These are just examples.

The materials of the first layer 44 and the second layer 46 may be selected to have good bonding characteristics between the two layers. Similarly, the material of the third layer 48 may be selected to have good bonding characteristics with the first and second layers 44/46. For example, a balloon 22 may be formed from a first layer 44 made from a hydrophilic polyether block amide and a second layer 46 made from a regular or non-hydrophilic polyether block amide. In some instances, the material of the third layer 48 may be the same as the material of the first layer 44, although this is not required. In other embodiments, a suitable tie layer (not illustrated) may be provided between adjacent layers. These are just examples.

In some instances, the addition of a third layer 48 may eliminate catch points created by the second layer 46 (in the absence of the third layer 48). For example, steps or lifted edges of the non-conductive coating 46 may cause device failure during insertion, withdrawal, or re-insertion of the device into a sheath or guide catheter. It is contemplated that the addition of the third layer 48 may smooth step-like transitions at the virtual electrode 28 as well as minimize lifted edges. The third layer 48, creating smoothed transitioning virtual electrodes 28, may also prevent the trapping of blood at between the virtual electrode and the tissue to be ablated. Trapped blood is theorized to result in premature device failure and the formation of coagulum due to a relatively lower impedance virtual electrode. In some instances, the third layer 48 may act as a strain relief by encasing the entire balloon 22, thus preventing the second layer 46 from splitting during inflation. It is further contemplated that the third layer 48 may act as an additional thermal barrier between the ablated tissue and the conductive first layer 44. This may allow the device 12 to be operated without circulating fluid for cooling, thus resulting in a more robust, lower profile device.

Prior to use, balloon 22 may be hydrated as part of the preparatory steps. Hydration may be effected by soaking the balloon in a saline solution. During ablation, a conductive fluid may be infused into balloon 22, for example via outlet 32. The conductive fluid may expand the balloon to the desired size. The balloon expansion may be monitored indirectly by monitoring the volume of conductive fluid introduced into the system or may be monitored through radiographic or other conventional means. Optionally, once the balloon is expanded to the desired size, fluid may be circulated within the balloon by continuing to introduce fluid through the fluid inlet 31 while withdrawing fluid from the balloon through the fluid outlet 32. The rate of circulation of the fluid may be between but not limited to 5 and 20 ml/min. This is just an example. The circulation of the conductive fluid may mitigate the temperature rise of the tissue of the blood vessel in contact with the non-virtual electrode areas.

Electrode 24 may be activated by supplying energy to electrode 24. The energy may be supplied at 400-500 KHz at about 5-30 watts of power. These are just examples, other energies are contemplated. The energy may be transmitted through the medium of the conductive fluid and through virtual electrodes 28 to the blood vessel wall to modulate or ablate the tissue. The second layer 46 of the balloon prevents the energy transmission through the balloon wall except at virtual electrodes 28 (which lack second layer 46).

Electrode 24 may be activated for an effective length of time, such as 1 minute or 2 minutes. Once the procedure is finished at a particular location, balloon 22 may be partially or wholly deflated and moved to a different location such as the other renal artery, and the procedure may be repeated at another location as desired using conventional delivery and repositioning techniques.

Disclosed herein are medical devices, balloons, and methods for making the same where one or more discrete balloon “virtual electrodes” are defined. The virtual electrodes are designed to dissipate or otherwise help to spread out forces that may tend to accumulate along the edge of the virtual electrode. In addition, the virtual electrodes may also help to more evenly distribute or otherwise spread current so that current accumulation along the edge of the virtual electrode can also be reduced. Some of these and other features are described in more detail herein.

In at least some embodiments, a mask may be utilized to manufacture a balloon 122 as shown schematically in FIGS. 5-9. In general, the process may result in a three layer balloon 122 having regions of two layers defining the balloon virtual electrodes. In the schematic drawings, other portions of the catheter or medical device that includes balloon 122 may also be seen. The other portions of the devices may or may not be present during the manufacturing process. The intent of showing these structures in the drawings is to demonstrate that balloon 122 may be used with medical devices such as those disclosed herein. In addition, balloon 122 may be utilized in medical devices such as device 12 (and/or other devices disclosed herein). Accordingly, the structural features of balloon 122 may be incorporated into device 12 (and/or other devices disclosed herein).

FIG. 5 is a side view of a portion of an example balloon 122. Balloon 122 may include a base or inner layer 144. In at least some embodiments, inner layer 144 may include a hydrophilic and/or conductive material such as those materials disclosed herein. A mask member 150 may be disposed on inner layer 144. The mask member 150 may vary but in some embodiments may include a masking tape or other suitable masking material. With mask member 150 in place, a coating 146 may be applied onto balloon 122 (e.g., onto inner layer 144) as shown in FIG. 6. In at least some embodiments, coating 146 may be applied by spray coating. Other methods may also be used including dip coating or the like. Coating 146 may include an electrically non-conductive and/or non-hydrophilic material such as those disclosed herein. After application of coating 146, mask member 150 may be removed, exposing a region 152 not coated with the coating 146 as shown in FIG. 7. Subsequently, one or more additional coating processes (conductive or non-conductive coatings) may be performed. For example, a second coating 148 may be applied onto balloon 122 (e.g., onto coating 146) as shown in FIG. 8. Coating 148 may also include a hydrophilic and/or conductive material such as those materials disclosed herein and may or may not be the same material as the base layer 144. After application of coating 148, an electrode or conductive region 128 is formed having two layers of conductive material, as shown in FIG. 9.

The process described above may result in a three layer balloon adjacent to conductive region 128 and a two layer conductive region 128. For example, the application of coating 148 may cover all of coating 146 and then become the outermost part of the virtual electrode 128 shown in FIG. 10. In some instances, the addition of the coating 148 over the virtual electrode 128 may eliminate catch points created by the second layer 146 (in the absence of the third layer 148). For example, steps in the outer layer or lifted edges of the non-conductive coating 146 may cause device failure during insertion, withdrawal, or re-insertion of the device. It is contemplated that the addition of the third layer 148 may smooth step-like transitions at the virtual electrode 128 as well as lifted edges. The third layer 148, creating smoothed transitioning virtual electrode 128, may also prevent the trapping of blood at between the virtual electrode 128 and the tissue to be ablated. Trapped blood is theorized to result in premature device failure and the formation of coagulum. In some instances, the third layer 148 may act as a strain relief by encasing the entire balloon 122, thus preventing the second layer 146 from splitting during inflation. It is further contemplated that the third layer 148 may act as an additional thermal barrier between the ablated tissue and the conductive base layer 144. This may allow the device 12 to be operated without circulating fluid for cooling, thus resulting in a lower profile device.

Numerous variations are contemplated for the process described above. For example, the shape, position, and/or configuration of mask member 150 may vary. For example, mask members 150 may have a circular, oval, polygonal, irregular, or other shape. The thicknesses, material composition, and other features of coatings 146/148 may also vary. In some embodiments, additional mask members may be utilized to form one or more additional conductive regions 128. In addition, additional masks and/or coating steps may also be performed.

In use, balloon 122 may be used in a manner similar to balloon 22. For example, balloon 122 may be attached to catheter shaft such as catheter shaft 34 and used for a suitable intervention such as an ablation procedure. During ablation, a conductive fluid may be infused into balloon 122 and an electrode positioned within balloon 122 (e.g., electrode 24) may be activated. The energy may be transmitted through the medium of the conductive fluid and through conductive region 128 to the blood vessel wall to modulate or ablate the tissue. Coating 146 may prevent the energy transmission through the balloon wall at locations other than conductive region 128.

FIG. 10 illustrates another example balloon 222 similar in form and function to balloons 22/122 discussed herein. The balloon 222 may include a base or inner layer. In at least some embodiments, the inner layer may include a hydrophilic and/or conductive material, such as those materials disclosed herein. An electrically non-conductive and/or non-hydrophilic material, such as those disclosed herein, may be disposed over the inner layer to form a second coating or layer 246. The second layer 246 may extend over the entire length of the balloon 222, although this is not required. The second layer 246 may be applied to the balloon 222 with a mask in place such that one or more regions 252 of the balloon 222 are not coated with the second layer 246. After removing the mask material, one or more additional coating processes may be performed. For example, a second coating 248 may be applied onto balloon 222 (e.g., onto coating 246) as shown in FIG. 8. Coating 248 may also include a hydrophilic and/or conductive material such as those materials disclosed herein and may or may not be the same material as the base layer. After application of coating 248, an electrode or conductive region 252 is formed having two layers of conductive material. In some instances, the coating 248 may cover only a portion of the balloon 222. For example, in some embodiments, the coating 248 may cover only the balloon body, as shown in FIG. 10. In other instances, the coating 248 may cover the entire balloon 222.

The materials that can be used for the various components of device 12 (and/or other medical devices disclosed herein) may include those commonly associated with medical devices. For simplicity purposes, the following discussion makes reference to device 12. However, this is not intended to limit the devices and methods described herein, as the discussion may be applied to other similar medical devices disclosed herein.

Device 12 may be made from a metal, metal alloy, polymer (some examples of which are disclosed below), a metal-polymer composite, ceramics, combinations thereof, and the like, or other suitable material. Some examples of suitable metals and metal alloys include stainless steel, such as 304V, 304L, and 316LV stainless steel; mild steel; nickel-titanium alloy such as linear-elastic and/or super-elastic nitinol; other nickel alloys such as nickel-chromium-molybdenum alloys (e.g., UNS: N06625 such as INCONEL® 625, UNS: N06022 such as HASTELLOY® UNS: N10276 such as HASTELLOY® C276®, other HASTELLOY® alloys, and the like), nickel-copper alloys (e.g., UNS: N04400 such as MONEL® 400, NICKELVAC® 400, NICORROS® 400, and the like), nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such as MP35-N® and the like), nickel-molybdenum alloys (e.g., UNS: N10665 such as HASTELLOY® ALLOY B2®), other nickel-chromium alloys, other nickel-molybdenum alloys, other nickel-cobalt alloys, other nickel-iron alloys, other nickel-copper alloys, other nickel-tungsten or tungsten alloys, and the like; cobalt-chromium alloys; cobalt-chromium-molybdenum alloys (e.g., UNS: R30003 such as ELGILOY®, PHYNOX®, and the like); platinum enriched stainless steel; titanium; combinations thereof; and the like; or any other suitable material.

As alluded to herein, within the family of commercially available nickel-titanium or nitinol alloys, is a category designated “linear elastic” or “non-super-elastic” which, although may be similar in chemistry to conventional shape memory and super elastic varieties, may exhibit distinct and useful mechanical properties. Linear elastic and/or non-super-elastic nitinol may be distinguished from super elastic nitinol in that the linear elastic and/or non-super-elastic nitinol does not display a substantial “superelastic plateau” or “flag region” in its stress/strain curve like super elastic nitinol does. Instead, in the linear elastic and/or non-super-elastic nitinol, as recoverable strain increases, the stress continues to increase in a substantially linear, or a somewhat, but not necessarily entirely linear relationship until plastic deformation begins or at least in a relationship that is more linear that the super elastic plateau and/or flag region that may be seen with super elastic nitinol. Thus, for the purposes of this disclosure linear elastic and/or non-super-elastic nitinol may also be termed “substantially” linear elastic and/or non-super-elastic nitinol.

In some cases, linear elastic and/or non-super-elastic nitinol may also be distinguishable from super elastic nitinol in that linear elastic and/or non-super-elastic nitinol may accept up to about 2-5% strain while remaining substantially elastic (e.g., before plastically deforming) whereas super elastic nitinol may accept up to about 8% strain before plastically deforming. Both of these materials can be distinguished from other linear elastic materials such as stainless steel (that can also can be distinguished based on its composition), which may accept only about 0.2 to 0.44 percent strain before plastically deforming.

In some embodiments, the linear elastic and/or non-super-elastic nickel-titanium alloy is an alloy that does not show any martensite/austenite phase changes that are detectable by differential scanning calorimetry (DSC) and dynamic metal thermal analysis (DMTA) analysis over a large temperature range. For example, in some embodiments, there may be no martensite/austenite phase changes detectable by DSC and DMTA analysis in the range of about −60 degrees Celsius (° C.) to about 120° C. in the linear elastic and/or non-super-elastic nickel-titanium alloy. The mechanical bending properties of such material may therefore be generally inert to the effect of temperature over this very broad range of temperature. In some embodiments, the mechanical bending properties of the linear elastic and/or non-super-elastic nickel-titanium alloy at ambient or room temperature are substantially the same as the mechanical properties at body temperature, for example, in that they do not display a super-elastic plateau and/or flag region. In other words, across a broad temperature range, the linear elastic and/or non-super-elastic nickel-titanium alloy maintains its linear elastic and/or non-super-elastic characteristics and/or properties.

In some embodiments, the linear elastic and/or non-super-elastic nickel-titanium alloy may be in the range of about 50 to about 60 weight percent nickel, with the remainder being essentially titanium. In some embodiments, the composition is in the range of about 54 to about 57 weight percent nickel. One example of a suitable nickel-titanium alloy is FHP-NT alloy commercially available from Furukawa Techno Material Co. of Kanagawa, Japan. Some examples of nickel titanium alloys are disclosed in U.S. Pat. Nos. 5,238,004 and 6,508,803, which are incorporated herein by reference. Other suitable materials may include ULTANIUM™ (available from Neo-Metrics) and GUM METAL™ (available from Toyota). In some other embodiments, a superelastic alloy, for example a superelastic nitinol can be used to achieve desired properties.

In at least some embodiments, portions or all of device 12 may also be doped with, made of, or otherwise include a radiopaque material. Radiopaque materials are generally understood to be materials which are opaque to RF energy in the wavelength range spanning x-ray to gamma-ray (at thicknesses of <0.005″). These materials are capable of producing a relatively dark image on a fluoroscopy screen relative to the light image that non-radiopaque materials such as tissue produce. This relatively bright image aids the user of device 12 in determining its location. Some examples of radiopaque materials can include, but are not limited to, gold, platinum, palladium, tantalum, tungsten alloy, polymer material loaded with a radiopaque filler, and the like. Additionally, other radiopaque marker bands and/or coils may also be incorporated into the design of device 12 to achieve the same result.

In some embodiments, a degree of Magnetic Resonance Imaging (MRI) compatibility is imparted into device 12. For example, device 12 or portions thereof may be made of a material that does not substantially distort the image and create substantial artifacts (i.e., gaps in the image). Certain ferromagnetic materials, for example, may not be suitable because they may create artifacts in an MRI image. Device 12 or portions thereof may also be made from a material that the MRI machine can image. Some materials that exhibit these characteristics include, for example, tungsten, cobalt-chromium-molybdenum alloys (e.g., UNS: R30003 such as ELGILOY®, PHYNOX®, and the like), nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such as MP35-N® and the like), nitinol, and the like, and others.

Some examples of suitable polymers for device 12 may include polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP), polyoxymethylene (POM, for example, DELRIN® available from DuPont), polyether block ester, polyurethane (for example, Polyurethane 85A), polypropylene (PP), polyvinylchloride (PVC), polyether-ester (for example, ARNITEL® available from DSM Engineering Plastics), ether or ester based copolymers (for example, butylene/poly(alkylene ether) phthalate and/or other polyester elastomers such as HYTREL® available from DuPont), polyamide (for example, DURETHAN® available from Bayer or CRISTAMID® available from Elf Atochem), elastomeric polyamides, block polyamide/ethers, polyether block amide (PEBA, for example available under the trade name PEBAX®), ethylene vinyl acetate copolymers (EVA), silicones, polyethylene (PE), Marlex high-density polyethylene, Marlex low-density polyethylene, linear low density polyethylene (for example REXELL®), polyester, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polytrimethylene terephthalate, polyethylene naphthalate (PEN), polyetheretherketone (PEEK), polyimide (PI), polyetherimide (PEI), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), poly paraphenylene terephthalamide (for example, KEVLAR®), polysulfone, nylon, nylon-12 (such as GRILAMID® available from EMS American Grilon), perfluoro(propyl vinyl ether) (PFA), ethylene vinyl alcohol, polyolefin, polystyrene, epoxy, polyvinylidene chloride (PVdC), poly(styrene-b-isobutylene-b-styrene) (for example, SIBS and/or SIBS 50A), polycarbonates, ionomers, biocompatible polymers, other suitable materials, or mixtures, combinations, copolymers thereof, polymer/metal composites, and the like.

It should be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps without exceeding the scope of the disclosure. This may include, to the extent that it is appropriate, the use of any of the features of one example embodiment being used in other embodiments. The invention's scope is, of course, defined in the language in which the appended claims are expressed. 

What is claimed is:
 1. A medical device for modulating nerves, the medical device comprising: an elongate shaft having a distal region; a balloon coupled to the distal region, the balloon having an inner conductive layer, an outer conductive layer, and an intermediate non-conductive layer disposed between the inner layer and the outer layer; an electrode disposed within the balloon; and a virtual electrode defined on the balloon, the virtual electrode including a conductive region defined along a first portion of the balloon that comprises the inner conductive layer and the outer conductive layer and is free of the intermediate non-conductive layer.
 2. The medical device of claim 1, wherein the outer conductive layer covers the entire balloon.
 3. The medical device of claim 1, wherein the outer conductive layer covers only a portion of the balloon.
 4. The medical device of claim 1, wherein the intermediate non-conductive layer has a substantially constant thickness.
 5. The medical device of claim 1, wherein the electrode includes a coil electrode helically disposed about the shaft.
 6. The medical device of claim 1, further comprising one or more additional virtual electrodes.
 7. The medical device of claim 1, further comprising a conductive fluid disposed within the balloon.
 8. A medical device for modulating nerves, the medical device comprising: an elongate shaft having a distal region and a fluid inlet and a fluid outlet proximate the distal region; a balloon coupled to the distal region, the balloon having an inner conductive layer, an outer conductive layer, and an intermediate non-conductive layer disposed between the inner layer and the outer layer; a helically wound electrode disposed along the elongate shaft and within the balloon; and a virtual electrode defined on the balloon, the virtual electrode including a conductive region defined along a first portion of the balloon that comprises the inner conductive layer and the outer conductive layer and is free of the intermediate non-conductive layer.
 9. The medical device of claim 8, wherein the outer conductive layer covers the entire balloon.
 10. The medical device of claim 8, wherein the outer conductive layer covers a portion of the balloon.
 11. The medical device of claim 8, wherein the intermediate non-conductive layer has a substantially constant thickness.
 12. The medical device of claim 8, further comprising one or more additional virtual electrodes.
 13. The medical device of claim 8, further comprising a conductive fluid disposed within the balloon.
 14. The medical device of claim 8, wherein the inner the outer layers comprise a hydrophilic polymer.
 15. The medical device of claim 14, wherein the hydrophilic polymer exhibits between 20% and 120% water uptake.
 16. The medical device of claim 14, wherein the inner and outer layers comprise a hydrophilic polymer selected from a hydrophilic polyurethane, a hydrophilic polyether block amide, a hydrophilic nylon and a hydrophilic polyester. 